This invention relates to fuel injectors, and more particularly, to fuel injectors having a sac volume that minimizes residual fuel after metering.
Fuel injectors are commonly employed in internal combustion engines to provide precise metering of fuel for introduction into each combustion chamber. Additionally, the fuel injector atomizes the fuel during injection, breaking the fuel into a large number of very small particles, increasing the surface area of the fuel being injected, and allowing the oxidizer, typically ambient air, to more thoroughly mix with the fuel prior to combustion. The precise metering and atomization of the fuel reduces combustion emissions and increases the fuel efficiency of the engine.
An electromagnetic fuel injector typically utilizes a solenoid assembly to supply an actuating force to a fuel metering valve. Typically, the fuel metering valve is a plunger style needle valve which reciprocates between a closed position, where the needle is seated in a valve seat to prevent fuel from escaping through a metering orifice into the combustion chamber, and an open position, where the needle is lifted from the valve seat, allowing fuel to discharge through the metering orifice for introduction into the combustion chamber.
Typically, a volumetric chamber or sac exists between the discharge tip of the needle and the metering orifice. Upon seating of the needle on the valve seat, a volume of fuel remains within the sac and tends to drain through openings in the metering orifice after the metered fuel has already been discharged through the metering orifice, typically during low manifold pressure, high injector tip temperature operating conditions. This discharge produces rich combustion which generates unwanted exhaust emissions and reduces the fuel efficiency of the engine. Some of the fuel, however, remains in the sac which vaporizes and causes rich/lean shifts and hot start issues which are undesirable.
It would be beneficial to develop a fuel injector in which the sac volume is minimized, reducing the amount of unmetered fuel in the sac after metering.
Briefly, the present invention provides a fuel injector for use in a fuel injection system of an internal combustion engine. The fuel injector includes a valve body, a valve seat, a metering orifice, a needle and a volume. The body has an inlet, an outlet and a longitudinal axis extending therethrough. The valve seat is located within the body and disposed proximate the outlet. The valve seat includes a valve seat orifice and a sealing surface surrounding the orifice. The metering orifice is connected to the body downstream of the valve seat. The needle is reciprocally located within the body along the longitudinal axis between a first position wherein the needle is displaced from the valve seat, allowing fuel flow past the needle, and a second position wherein the needle is biased against the valve seat, precluding fuel flow past the needle. The needle includes a first portion having a first cross-sectional area and a second portion having a second cross-sectional area. The second cross-sectional area is larger than the first cross-sectional area. The second portion includes an end face extending generally perpendicular to the longitudinal axis. The end face is located upstream of the valve seat orifice. The volume is generally defined by the metering orifice, the end face and the valve seat orifice when the needle is in the second position.
The present invention also provides a fuel injector for use in a fuel injection system of an internal combustion engine. The fuel injector comprises a valve body, a valve seat, a metering orifice, a needle, and a volume. The body has an inlet, an outlet and a longitudinal axis extending therethrough. The valve seat is located within the body and disposed proximate the outlet. The valve seat includes a valve seat orifice and a sealing surface surrounding the valve seat orifice. The metering orifice is connected to the body downstream of the valve seat. The needle is reciprocally located within the body along the longitudinal axis between a first position wherein the needle is displaced from the valve seat, allowing fuel flow past the needle, and a second position wherein the needle is biased against the valve seat, precluding fuel flow past the needle. The needle includes a first portion having a first cross-sectional area and a second portion having a second cross-sectional area. The second portion includes an end face extending generally perpendicular to the longitudinal axis. The volume is generally defined by the metering orifice, the end face and the valve seat orifice when the needle is in the second position. The metering orifice is spaced from the end face by a distance of between 100 microns and 250 microns.
The present invention also provides a method of reducing unmetered fuel in a fuel injector. The fuel injector including a valve seat, a needle, a volume, and a metering orifice. The method comprises the steps of providing a fuel injector; providing pressurized fuel to the fuel injector; opening the fuel injector by moving the needle off of the valve seat, thereby allowing the pressurized fuel to flow past the needle and the valve seat and through the volume and the metering orifice for ejection from the fuel injector; and closing the fuel injector by seating the needle against the valve seat, reducing the volume and fuel within the volume.